I guess this is more academic (and will require practical verification by lau chiaus in the know) but for the benefit of interested parties:
List of gangs and places they (still?) own in Singapore:
From 21 :
Ang Meng Tong
Di Ang Ying
Ang Yee Tong
Tiong Yee Tong
Pa Hai Tong
Ghee Meng Tong
Ghee Hin Kongsi
Ghee Hock (Part of Ghee Hin Kongsi)
Ang Guat Hwei
Ang Tian San
Feng Huang Shan (Yishun/ang mo kio)
Feng Qing Shan
Guat San Sia (Known as moon sect few years back)
Deet San Sia
Leng Heng Sia
Yee Pak Hai
Yee Chuan San
Yee Chuan Hai
Yee Hup Ho
Tiong Meng Ko
Heng Kee
Gnoi Seek Kee
Hup Ho Tong
21 San[213]
21 Hai
21 Ang Hai
21 Re Yue Ban
Ang Soon Tong (Sembawang but inactive)
From 369(Salakau/Sio kun tong) :
Kallang Airport (Kallang)
Tanglin Halt
Mei Ling Lor
Queenstown Chao (Obvious)
Tanjong Rhu (Raffles place? (Not confirmed))(Quite active)
"Lak Ko"- 6th Avenue
"Chit Ko"- 7th Avenue
Taman Selasih
"Goh Cho Bay"- Rochor Bay
Teck Whye Lane (Choa Chu kang)
Yew Tee
Kim Boon Tai
Toa Payoh Chao (Obvious) (Quite active)
Marsiling Chao (Obvious)
Tampines Chao (Obvious)
"Ang San"- Redhill (Obvious)
Hougang Chao (Obvious)
Chao Lak Ho
Sin Ming Lor/Sin Ming Road (Bishan) (Quite active)
Anak 537 (Tampines, Bedok, pasir ris)
From 18 (zhup puay siao) :
Sio Yi Ho (Most active)
Hup Soon Heng
Siao Kim Tian
Ar Bak Kuay (Quite active)
Aljunied Cresent Siao (Obvious)
Toa Payoh Siao (Obvious)
Bugis Siao (Obvious)
Kranji Siao (Obvious)
3 Beh Lor
4 Beh Lor
7 Beh Lor
Rochor Siao (Obvious)
Bedok Siao (Obvious)
Depot Siao
Purmei Siao
Hougang Siao (Obvious)
Geylang Siao (Obvious)
Liew Lian Ka
Telok Blangah Cresent Siao
Tampines Siao (Obvious)
Tekka Siao
Mai Siao Siao (Most inactive)
Sio Ka Po
From 04 Gang : (Inactive)
Wah Kee (华记)
China Town 04
From 24 (Ji Si) :
Ghee Hai Kim (义海金) (Most people)
Ghee Lian Hor (Active)
Ghee Leng Kiat
Patt Leong
Sio Ang Kun (Most little people)(Bedok, Ang mo kio)(Just re-created cause it was inactive)
Sio Lo Kuan (Active)(Deskar road)
08 (Kong Pui) :
Hai Lok San (108) (海陆山)(Old gang)
Hai Lok You
Pek Kim Leng (白金龙)
Pek Ka Long
Kim Leng Hor (金龙虎)
Sio Leng Hor (小龙虎)
Di Chet (27)(Inactive)
Go Hock San
Go Kong Go (505)(Inactive)
Sio Ang Leng
Leng Hor Shan
Sio Oh Leng
Pui Kong Pui(808)
Sio Pa Leng San
Sa Kong Sa (303)(Quite Active)(Teck whye lane)
There are 2 other gangs :
Sarajumbo(Indian Gang)
Omega(Malay Gang)(Hangs out at Downtown East)
.